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Hunting the biggest atoms in the universe

By Tim Dean

IN APRIL, the Israeli scientist Amnon Marinov announced that he had glimpsed a mysterious island. It was something that he and many rival explorers had long been seeking – but few of those rivals were prepared to accept that he had really found what he said he’d found. Yet if he is right, physicists may have to reconsider what they know about the outer limits of matter.

What Marinov of the Hebrew University of Jerusalem and his colleagues claim to have discovered is a monstrous atom with by far the heaviest nucleus ever seen, packing a whopping 122 protons and 170 neutrons. Crucially, the team had not synthesised it in the lab, but found it in nature, in a sample of purified thorium. The discovery implied that the element had a half-life of no less than 100 million years (www.arxiv.org/0804.3869).

Had his team finally stumbled upon the fabled “island of stability” – a region populated by superheavy atoms that is widely believed to exist beyond the outer reaches of the periodic table? Possibly, but a key problem for Marinov’s atomic giant is that 100-million-year half-life. “It couldn’t be shorter or we wouldn’t see it,” he explains. This is incredibly long for such a massive element, and goes against the theoretical grain. No wonder his claim has been viewed with scepticism.

The island of stability is no flight of fancy, though. It is predicted by well-established theory, the same theory that casts doubt on Marinov’s claim. By smashing atomic nuclei together, some of the rival teams have synthesised elements just a handful of protons short of Marinov’s purported record-breaker. …